1. Technical Field
This disclosure relates generally to electronic circuits and, in particular, to circuits for frequency mixing.
2. Description of the Related Art
Wireless devices are becoming more and more popular as mobile communications and computing devices become ubiquitous. Some wireless devices use radio frequency communications to operate. In such wireless devices, radio frequency upconverters or mixers are important components.
Conventional upconverter or mixer circuits are used to convert a baseband signal to a transmission band signal by mixing the baseband signal with a carrier signal. In a conventional upconverter/mixer circuit, DC offsets of circuitry driving the mixer, as well as a DC offset in an input stage of the mixer, contribute to generation of carrier leakage. This leakage can corrupt the modulation or otherwise lead to non-compliance with specifications for standardized systems such as wireless networks and cell phones.
In order to reduce such offsets, the devices in the circuit are made large to improve matching. This large size leads to large die area, increased costs, and increased power consumption. Furthermore, in many RF mixers, it is not practical to sense the DC offset at the output, as such circuitry would unduly load the circuit.
As a result, there remains a need for an improved mixer circuit.